1. Field of the Invention
The present invention relates to a method of changing die assemblies for a press machine.
2. Description of the Relevant Art
Japanese Patent Application No. 62-2876 filed by the same assignee as the present invention discloses a press machine having a plurality of mobile bolsters movable in a direction normal to the direction in which workpieces are transferred. One or more die assemblies include a lower die or lower dies mounted on the upper surfaces of the mobile bolsters and arranged in a row along the workpiece transferring direction. Workpieces are placed on the lower dies and simultaneously pressed, e.g., drawn, trimmed, and punched, by upper dies supported on respective die holders and lowered toward the lower dies. Thereafter, the workpieces are simultaneously set on the next lower dies by a transfer device and then pressed again.
The workpiece transfer device comprises a plurality of hydraulic lifting/lowering units disposed on opposite sides of the die assemblies, vertically movable bars supported on the lifting/lowering units and vertically movable thereby, and feed bars movable back and forth along the vertically movable bars by suitable means. Between the feed bars, there are coupled and extend a plurality of handling bars each supporting a plurality of workpiece holders for holding workpieces under suction. During one pressing cycle, the handling bars are located in retracted positions between the die assemblies. Each time one pressing cycle is completed, the vertically movable bars and the feed bars are operated together to transfer the pressed workpieces to the respective next die assemblies. Handling bar gripping devices are mounted on each of the mobile bolsters at opposite ends thereof. When replacing the die assemblies, the handling bars are removed from the feed bars, and the opposite ends of the handling bars are gripped by the handling bar gripping devices. The mobile bolsters with the die assemblies and handling bar gripping devices being supported thereon are moved out of the press machine.
In the press machine, the die assemblies are closely positioned in order to make the overall size of the press machine compact and to shorten the time in which to transfer the workpieces. Since, however, the handling bar gripping devices are disposed between the closely arranged die assemblies, parts of the handling bar gripping devices and the workpiece holders are positioned in physical interference with the die assemblies as they are taken into and out of the press machine.